You should first check the rangefinder with a lens that you know focuses well. Most likely, the rangefinder is off, as this is the most obvious cause. Then, you should check your lenses. The LTM ones are often all over the place, also because of the adapters.

sounds like a rangefinder misalignment to me. Try with other lens focusing at infinity objects to see if things align (i always aim for the roof of the tallest building). i have the biogon as well and since it's a 21mm, i dont even use the patch and guess all the time. mine has issues focusing a 50 lux but no issues with the cron.

Most lenses suffer sometimes of "focusing glitches" even leitz lenses. If you want to be sure you have your set-up propely aligned, you should first have your bodies calibrated, prefarably by a qualified service technican in a collimator. Both the Voigtländer and Zeiss M lenses are reasonably easy to adjust, just shims between the lens cluster and focusing helicoil. The leitz lenses have to be sent to factory...VERY expensive ! The reason here is that in the past, with film bodies, this was not an issue, but with digital bodies it is...

I wonder if it's really the rangefinder as "woonder" writes that he's fine with three of his lenses. If the RF is misaligned, wouldn't that mean that all of those well working lenses are exactly misaligned in the same way and the same degree? How likely is that?

My M8 works perfectly with my Heliar 15, my Ultron 28, my Summitar 50, my Heliar 75 and even with my Elmar 90. Gosh, I can even use my Hektor 135 on that M8 and get sharp pictures. But an Ultron 35 I recently tried was impossible to focus properly.
A short test on my NEX-7 (with live view and peaking) showed that the Ultron 35 had a problem.

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